The present invention relates to satellite communication systems; and, more particularly, to an apparatus and method for determining an operating point of a high power amplifier (HPA) by adding a direct current (DC) voltage converting block to a channel amplifier located at a front-end of the high power amplifier and using signal information outputted from the DC voltage converting block, and a computer readable recording medium on which a program implementing the method is recorded, wherein the operating point relates to a downlink signal transmitted from a communication and broadcasting satellite to the earth.
For any transponder""s channel, since an operating point of a high power amplifier changes depending on the intensity variation of a signal transmitted from an earth station to a satellite which is due to operating changes of self transmit power of earth stations sharing a certain transponder""s channel, the number of carriers, atmospheric changes depending on the rainfall and so on, a ground monitoring center should check the operating point of the high power amplifier in real-time.
In the meantime, a system and method for determining an operating point of a nonlinear high power amplifier operating in a satellite is described in U.S. Pat. No. 5,731,993, entitled xe2x80x9cNonlinear Amplifier Operating Point Determination System and Methodxe2x80x9d and issued on Mar. 24, 1998. As shown in this patent document, in order to determine an operating point of a high power amplifier within a transponder, a test signal source is embodied in a front-end of a high power amplifier corresponding to each channel and a summing circuit is further employed to combine the test signal source and a main signal source. As a result, a signal analyzer equipped in the transponder determines the operating point by using a signal provided from an output multiplexer. Further, by placing an additional antenna in a satellite and receiving a signal source delivered from a transmit antenna, the signal analyzer interprets the received signal.
However, in the above two cases, additional electrical devices should be equipped in the satellite, which leads a non-economical influence, and the introduced method can extract the operating point only in the time division multiple access (TDMA) scheme.
Currently, it is difficult on the earth to directly and exactly detect an output power of a high power amplifier in a satellite located on a stationary orbit at an altitude of 36,000 km above the ground since there are operating environment changes of the high power amplifier, transmission loss changes depending on the rainfall, an error of a power measuring system and so on. To overcome the drawbacks, the high power amplifier transmits a telemetry signal related to an output level to a ground monitoring center which checks a state of the high power amplifier by using the telemetry signal. The communication and broadcasting satellite uses a traveling wave tube amplifier (TWTA) as the high power amplifier and, in this case, the operating point and the output power level of the high power amplifier are measured by utilizing telemetry of anode voltage or Helix current. However, practically, it deteriorates discrimination in determining the output level of the high power amplifier.
It is, therefore, a primary object of the present invention to provide an apparatus and method for determining an operating point of a high power amplifier by adding a direct current (DC) voltage converting block to a channel amplifier located at a front-end of the high power amplifier and using signal information outputted from the DC voltage converting block, and a computer readable recording medium on which a program implementing the method is recorded, wherein the operating point relates to a downlink signal transmitted from a communication and broadcasting satellite to the earth.
In accordance with one aspect of the present invention, there is provided an apparatus for determining an operating point of a high power amplifier, comprising:
direct current (DC) voltage converting unit for coupling an output power of a channel amplifier and converting the coupled output power to a DC voltage;
storing unit in a ground monitoring center for, before satellite launching, for whole channels of a satellite transponder, mapping the output power value of the high power amplifier and the DC voltage level of the channel amplifier per each command step assigned to either a fixed gain mode (FGM) or an automatic level control (ALC) mode and storing mapped results; and
operating point detecting unit in the ground monitoring center for, after the satellite launching, detecting the operating point and the output power level of the high power amplifier of a corresponding channel based on the mapped results stored in the storing unit by using the DC voltage level measured at the DC voltage converting unit as telemetry information.
In accordance with another aspect of the present invention, there is provided a method for determining an operating point of a high power amplifier for use in a satellite communication system, which comprises the steps of:
(a) employing a circuit for converting an output power level of a channel amplifier to a direct current (DC) voltage within the channel amplifier so as to detect an operating point of the high power amplifier and a transmit power level of each channel for a down link signal transmitted from a satellite to an earth station;
(b) before satellite launching, when testing each command step of the channel amplifier, measuring a DC voltage according to the output power level of the channel amplifier in a fixed gain mode (FGM) and an automatic level control (ALC) mode and producing a mapping table by mapping the output power value of the high power amplifier and the DC voltage value of the channel amplifier; and
(c) after the satellite launching, determining the operating point and the output power level of the high power amplifier for a corresponding channel based on the mapping table by using the DC voltage level measured at the DC voltage converting circuit as telemetry information.
In accordance with still another aspect of the present invention, there is provided a computer readable medium on which a program used in implementing a high power amplifier operating point determination method for use in a satellite communication system employing a processor is recorded, comprising:
first program instructing function for, to detect an operating point of a high power amplifier and a transmit power level of each channel for a down link signal transmitted from a satellite to an earth station, before satellite launching, when testing each command step of a channel amplifier, measuring a DC voltage according to an output power level of the channel amplifier in a fixed gain mode and an automatic level control mode and producing a mapping table by mapping the output power value of the high power amplifier and the DC voltage value of the channel amplifier; and
second program instructing function for, after the satellite launching, determining the operating point and the output power level of the high power amplifier for a corresponding channel based on the mapping table by using the DC voltage level measured at a circuit for converting the output power level of the channel amplifier to a DC voltage as telemetry information.
The present invention uses information of a channel amplifier located in an front-end of a high power amplifier so as to detect a transmit power level for each channel and operating point information of the high power amplifier for a downlink signal transmitted from a satellite to an earth station, and adds a circuit for converting an output power level of the channel amplifier to a DC voltage to an RF circuit of the channel amplifier to thereby use the information outputted from the channel amplifier as telemetry. Then, before satellite launching, the DC voltage is measured according to the output power level of the channel amplifier for a fixed gain mode and an automatic level control mode when testing the channel amplifier and a database is made of information for the output power values of the channel amplifier and the high power amplifier for the two modes. As a result, after the satellite launching, a ground monitoring center can measure the operating point and the output level of the high power amplifier by only analyzing the DC voltage information of the channel amplifier among the telemetry signals transmitted from the satellite.
That is to say, the present invention detects the operating point of the high power amplifier by using the output power information of the channel amplifier located in an front-end of the high power amplifier and adopts a scheme of utilizing the correlativity between the output power value of the high power amplifier and the DC voltage information acquired by coupling the output power of the channel amplifier to an internal circuit and converting the coupled power value to a DC voltage when manufacturing the channel amplifier.
Therefore, it is possible to allow a system operator to notice the operating point and the output level of the high power amplifier by using the DC voltage information as a telemetry signal and making the ground monitoring center interprets the DC voltage telemetry information. Further, the satellite system can be effectively managed by sending a new command signal to the channel amplifier according to the operational environment of the satellite system. This can be also used as a back-up when the telemetry of the high power amplifier has errors.